They burst in shortly after the pizzeria had closed for the night on Thursday December 13.
West Yorkshire Police said:-
"Police are investigating following an armed robbery at Pizza Express last week in Leeds.
"The incident happened on Thursday 13 December; officers were called at 23:18 to the premises on Street Lane where three males walked in, one carrying a knife.
"Cash was taken from the premises and no one was injured during the incident.
"The suspects fled the scene.
"Anyone who witnessed the incident or has any further information is asked to contact the police via 101 quoting crime reference number 13180625046 or information can be passed to Crimestoppers anonymously on 0800 555 111."